This invention relates to inking mechanism for a printing press, and particularly to an improved ductor apparatus of the oscillating type which is adapted to transfer a "stripe" of ink from a fountain roll to the first of a series of distributor rolls from whence the ink is eventually applied to a printing plate. Particularly in lithographic printing presses the ink employed is a rather thick viscous grease-like material which must be precisely metered and distributed in order to achieve uniform proper inking of the printing plate.
A typical ink fountain includes a fountain roller which may be driven at variable speeds, and which is mounted to form one wall of the ink fountain which holds a supply of the thick viscous ink. Sides of the fountain confine the ink within the length of the fountain roll, and the bottom of the fountain is conventionally formed by a flexible blade or plate which extends upwardly and away from adjacent the lower end of the fountain roll, between the sides. The framework of the fountain supports a number of adjusting thumb screws which press against the edge of the blade, near the fountain roll, in order to adjust that edge precisely with respect to the surface of the fountain roll and thereby to control precisely the metering edge or slit between the blade and the roll, through which the film of ink is formed on the fountain roll. During makeready operations, the press operator adjusts these thumb screws while observing the thickness and continuity of the film of ink on the fountain roll, in order to achieve the desired film of ink thereon.
During press operation the ductor roll is oscillated such that a portion of its surface first contacts the fountain roll and picks up a "stripe" of ink, and then the ductor roll is moved away from the fountain roll and into contact with the first distributor roll, where the stripe of ink is applied to the distributor roll, and through the succession of distributor rolls and vibrating rolls making up the inker (sometimes called the inking tower) which carries the ink to the plate. Mechanism for oscillating the ductor is conventionally provided in the form of oscillating links, including pivoted arms carrying opposite ends of the ductor roll and connected to cam mechanism which controls the motion of the ductor. This linkage includes adjustments for controlling precisely the contact of the ductor with the first distributor roll, and also contact between the ductor and the fountain roll.
During makeready operations the fountain blade is set relative to the fountain roll with adjustable thumb screws to provide the correct amount of ink supply to the plate on the press. Areas on a plate with heavy coverage require more ink than area with light coverage. This adjustment is accomplished while the ductor roll is set against the fountain roll and the thumb screws are adjusted while the pressman observes the ink film formed on the fountain roll.
There are two ways to achieve the desired ductor position during this operation. One is to stop the press with the ductor roll against the fountain roll, then turn the fountain roll manually during the adjusting operation. Many presses have a ratchet-lever and overrunning clutch for this purpose. On wide presses, particularly using viscous inks, it is difficult to turn the fountain roll by hand, even with such lever mechanism.
Some presses are provided with an auxiliary drive for wash-up and makeready operations. For example, in a multi-color press with a main line shaft drive, clutches are provided to disengage each impression cylinder from the line shaft. Auxiliary drive motors are connected through suitable clutches to each plate cylinder, and through the gearing drive the blanket cylinders and other rollers, etc., of the associated inker. Where motor driven dampener rollers are used, this same motor may function as the auxiliary motor.
During makeready, the auxiliary drive motor is used to rotate the inker, but this also oscillates the ductor and loads up the inking rollers since the press is off impression. This results in a considerable power demand on the auxiliary motor, sometimes overloading it, and after makeready the inking rollers have to be washed up before printing can begin.